Arctic sea ice is on pace for a record-setting retreat this summer, which would be the sixth straight year for a major meltdown far in excess of the historical average.

The U.S. National Snow and Ice Data Center (NSIDC), the leading monitor of the state of the Arctic Ocean's ice cover, has released new data showing the still-frozen portion of the polar sea has shrunk to an end-of-June low of about 10 million square kilometres.

The latest evidence of sustained and transformative change to the Arctic environment comes at a time when newly released documents show federal Environment Minister Peter Kent was given a detailed briefing — by federal officials anticipating media attention — on last year's 40-year "record low" end-of-summer ice cover in the Canadian Arctic.

Ice in Canadian waters had retreated by mid-September 2011 to 351,359 square kilometres, states the document, dated Oct. 3, 2011 and released this month to Postmedia News under the Access to Information Act.

The average minimum since 1971 is 838,348 square kilometres, it added.

"A reduction in the amount of sea ice in the Canadian Arctic Archipelago does not mean that hazards do not exist," the briefing note warned. "Icebergs, ice shelf fragments, ice islands, remnants of ice ridges and old ice floes are freely moving throughout the area. These features can be significantly more dangerous to marine interests than sea ice" and require "extreme caution while navigating in their vicinity."

The latest NSIDC data suggests the Arctic is facing yet another deep meltdown this summer.

A mid-June report by the Colorado-based NSIDC had already shown that the 2012 spring retreat — driven by a high-pressure system over the Beaufort Sea and by wind patterns and ocean currents that helped produce huge areas of open water throughout the Arctic — saw the disappearance of nearly one million more square kilometres of ice than had melted by mid-June 2007.

That was the year scientists recorded the biggest end-of-summer retreat — down to just 4.13 million square kilometres by September 2007 — since the start of the satellite era more than 30 years ago.

The 2007 meltdown — which coincided with a Russian submersible's controversial planting of a flag on the North Pole seabed — put an unprecedented spotlight on the rapidly warming Arctic environment and triggered climate-change alarms around the world.

Despite some variation in the intensity of the annual Arctic ice retreat since then, the five greatest summer meltdownsin the 33-year history of satellite monitoring has occurred in past five melt seasons.

Scientists believe the ongoing loss of older, thicker ice — along with the increased transformation of the reflective, white surface of ice to heat-absorbing dark water — is creating a feedback loop that leads to ever-thinner ice cover and faster, more intense thaws each year.

But the NSIDC's June 19 report, while highlighting the "unusually rapid ice loss to this point," also cautioned that "it is still early in the melt season." The centre noted that "changing weather patterns throughout the summer will affect the exact trajectory of the sea ice extent" by the end of the summer of 2012.

Last year, reporting on what may have been an ecological first since the end of the last Ice Age some 10,000 years ago, a team of Danish and American scientists documented how bowhead whales from the separate Pacific Ocean and Atlantic Ocean populations had crossed paths in the Canadian Arctic.

The researchers described the phenomenon as one of the clearest signs yet that reduced ice cover in the Northwest Passage is opening a long-closed corridor and re-connecting two of the Northern Hemisphere's biological solitudes.

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